A spectrally controlled light source includes a light source with a spectral distribution repeated with a predetermined spatial period along an input plane so as to produce multiple copies of the spectral distribution separated by the spatial period. All copies are propagated through dispersive optics to produce equally dispersed spectra on an image plane. A periodic modulating element with a given filter period is applied to each of the dispersed spectra to produce corresponding modulated outputs. According to the invention, the spatial period of the light source on the image plane and the filter period of the modulating element are selected so as to produce a resonance effect that greatly enhances the utility of the spectrally modulated source.